PREPARE THE CAKE LAYERS: Preheat the oven to 350 F. Line two 9-inch round cake pans with waxed paper; butter and flour the pans; tap out any excess flour. In a mixer bowl, beat the butter until light and fluffy. Gradually add the sugar and continue beating until smooth. One at a time, beat in the eggs until well-blended. Sift together the flour, cocoa, baking soda, baking powder and salt. Add to the egg mixture in thirds, alternating with the milk, mixing only until blended. Blend in the vanilla and liqueur. Divide the batter between the two prepared pans. Bake until the tops of the cakes are springy to the touch, 40 to 45 minutes. Remove from the oven and set on racks to cool for 30 minutes. Loosen the edges with a knife and unmold. Peel off the waxed paper. Set the cakes on a rack and let cool completely. PREPARE THE FILLING: Combine the sugar, cream, chocolate and corn syrup in a small heavy saucepan. Bring to a simmer over moderate heat, stirring frequently. Reduce the heat to low and cook for 10 minutes, or until the mixture thickens. Remove from the heat, dot the top with the butter and let cool to room temperature, about 15 minutes. When cool, stir in the butter until the fudge filling is smooth and creamy. PREPARE THE CHOCOLATE CREAM: Beat the cream and cocoa until soft peaks form. Gradually add the confectioners' sugar and continue beating until stiff. ASSEMBLE THE CAKE: Cover one cake layer with all of the fudge filling. Sprinkle evenly with the chocolate chips. Spread 1/2 cup of the chocolate cream on top of the chips. Top with the second cake layer and cover the top and sides of the cake iwth half of the remaining chocolate cream. Use the remainder in a pastry bag to decorate the cake as desired. Refrigerate for up to 3 hours before serving time. PREPARE THE SYRUP: Combine the cocoa, corn syrup, sugar and 2 tablespoons of water in a small heavy saucepan. Bring to a simmer over low heat and cook, stirring constantly, for 2 minutes. Transfer the syrup to a small bowl and let cool to room temperature, stirring once or twice, to prevent a skin from forming. Just before serving, drizzle the syrup over the top of the cake in a lacy design.